In many fields, it is necessary or desirable to agglomerate finely divided particulate solid materials, that is, to cause the fine particles to associate into aggregate particles of larger size. By agglomeration, it is possible to render finely particulate materials more dispersible in liquids, to convert particulate materials to a desired average particle size or to a predetermined particle size range, to control the bulk density of a finely particulate product, and to achieve a more intimate combination of different ingredients than is practical by, e.g., dry blending. Agglomeration is particularly necessary in connection with processes which manufacture particulate products, of which juice crystals are typical, in such fashion that a significant proportion of the product is in the form of fines and, being of too small particle size to be included in the salable product, must be recycled to the process unless the particle size can be increased by agglomeration.
While some particulate materials exhibit an inherent tackiness or adhesive character adequate to provide the inter-particle adherence necessary for agglomeration, the materials to be agglomerated are more frequently dry, free-flowing powders. For agglomerating such materials, it has long been the practice to add to them a liquid agglomerating agent, i.e., a liquid which will wet the particle surfaces in such manner as to promote inter-particle adherence when a mass of the particles is agitated. The liquid employed to wet the particles is usually water, introduced as a spray or mist or in the form of steam. Though the art of agglomeration is quite old and highly developed, no method has heretofore been proposed and adopted for agglomerating the usual free flowing powdery solids which does not depend upon the introduction of extraneous moisture, either in the form of a spray or mist or as steam.
Agglomerating methods based on introduction of extraneous moisture have achieved considerable success, particularly with materials which agglomerate with relative ease when moistened. However, such methods present problems even under favorable circumstances, and there has been a continuing need for improvement in the art. One such problem arises from the difficulty of adding the moisture in such fashion that surface moisture adequate for inter-particle adherence is applied substantially uniformly to all of the particles. It is also frequently difficult to accomplish adequate wetting of the particulate material within the time allowable for agglomeration. Additionally, there are finely particulate materials which do not agglomerate satisfactorily by the methods of the prior art even when adequate wetting of the material is achieved. Further, most agglomeration methods require drying of the agglomerated product to remove moisture added for agglomeration.